Almost two-thirds of riders said taxis typically took more than 10 minutes to arrive at their homes during daytime on weekdays, while only about 10 percent ever had to wait that long for an on-demand ride service, according to the study. At night and on weekends, only 16 percent got a dispatched taxi in less than 10 minutes, while nearly 90 percent got an on-demand service in under 10 minutes.

"That's partially because taxis are really constrained by regulations; there aren't enough taxis to respond to the demand," said Lisa Rayle, a doctoral candidate in city planning at Berkeley, who led the study.

Overall, the study confirmed some stereotypes about the ride services: Passengers tend to be young, well-educated people seeking speed and convenience.

Researchers conducted spring interviews in three "hot spots" for ride services - the Mission, Marina and North Beach neighborhoods - including passengers who had just emerged from a ride-service car, as well as passersby (respondents who were in a hurry completed survey questions online). The report compared the data to a San Francisco Municipal Transportation study of taxi users conducted a year earlier, as well as trip logs from a medium-size San Francisco taxi company, and the 2012 American Community Survey.

The study, available at http://tinyurl.com/mo45uyk, is among the first to assess how the smartphone-summoned services - which researchers dubbed "ride sourcing" - affect taxis, public transit and car use.

Among its findings:

Market share. Uber commanded the lion's share of on-demand rides in San Francisco, accounting for 61 percent of rides, the majority of those through its lower-cost UberX service. Archrival Lyft had 30 percent, while Sidecar had 7 percent, the study found. Other services accounted for the remainder.

Why ride? Speed and convenience were the main reasons that respondents chose on-demand services. They cited ease of paying, shorter waits, faster rides and ease of summing a ride.

A fifth said they wanted to avoid drinking and driving, almost as many appreciated not having to park - two reasons that would hold equally true for taxis or public transit.

Competition with taxis and transit. Almost all survey respondents - 92 percent - said they would have made the same trips with or without Uber/Lyft/Sidecar. But if the services weren't available, 39 percent of those respondents instead would have taken a cab, 33 percent would have used public transit, and 6 percent would have driven. The rest would have found other means.

"While ride sourcing has similar demand to taxis in terms of types of trips, length of trips and destinations, there's evidence that people are using it much more than they used to use taxis," Rayle said. "It's expanded the range of places and times of day they're able to move around."

Ride services both complement and compete with public transit, the study found. A third of respondents otherwise would have used transit, and often chose ride services because they are faster - transit would have required transfers, for instance. While the survey didn't ask about connections to public transit, 4 percent of respondents said they were riding to or from a transit station. "We have some evidence it's working to solve that 'last mile' problem," Rayle said.

Car use. Proponents of ride services, including Uber CEO Travis Kalanick, claim that they will someday reduce car ownership. The survey found no evidence of that happening. However, it did find that the services allowed 40 percent of respondents to drive less frequently.

"It's still very early days" for the services to impact car ownership, Shaheen said. Her studies on member-based car-rental services like City CarShare looked at their impact on car ownership after they were in use for eight years, and found that average vehicles per household dropped from 0.47 to 0.24. Most of that shift came from one-car households going carless.

Demographics. Passengers in on-demand ride services were generally younger and better-educated than San Francisco's average population. A total of 57 percent were ages 25-34, while only 22 percent of San Francisco's population falls in that range.

More than four-fifths of respondents had bachelor's or graduate degrees, versus only 54 percent of the city's generation population.

Overall, the riders' income matched the income distribution for San Francisco, with one key exception: There were fewer low-income people. Only 9 percent of riders earn less than $30,000 a year, while 26 percent of San Franciscans fall into this category.

The surveyed riders tended to live in affluent areas, such as the Marina, Russian Hill, Nob Hill and the Castro - although that was skewed by the neighborhoods where the surveys were conducted, Shaheen cautioned.

The study didn't look at one key difference between taxis and ride services: disability access. San Francisco's taxi fleet includes 100 wheelchair-accessible cabs, which are a significant component of the city's paratransit. Uber, Lyft and Sidecar have merely said that they hope to find ways to offer accessible vehicles. Disabled-rights activists worry that the systems' growing popularity could leave them sidelined.

"While that wasn't something we looked at in this study, I do think it's an important point," Rayle said.

Both Shaheen and Rayle cautioned that the survey methodology means respondents weren't completely representational and that further research is warranted.

"There are a lot of fascinating areas, like energy and environmental impacts, to explore," Shaheen said.